A hacker named Steven has posted a video of Ice Cream Sandwich running on the Kindle Fire, along with more information in the XDA Developers forums. The hack is incomplete, lacking support for audio, Wi-Fi, the accelerometer and the light sensor. Also, transitions look a bit choppy, but it's a start.
The hacker plans to start an open source project for Ice Cream Sandwich on the Kindle Fire, and will post his code to it. This was only a matter of time, considering the android 4.0 code is open source.

Hackers have taken a keen interest in the Kindle Fire, probably due to its $200 price tag, dual-core processor and popularity among consumers. Shortly after its launch, users figured out how to root the tablet and install the Android Market, freeing themselves from the Amazon Appstore's smaller catalog. For users who want a more typical Android experience on the Kindle Fire, CyanogenMod 7 is also available as an alternative to Amazon's highly customized interface.